This invention relates to a stent with a discontinuous expandable wall comprising on at least a portion of its length a continuous covering layer of elastic material with an outer surface surrounding the discontinuous wall. This invention also relates to methods for applying such a layer on a stent.
The discontinuous walls of stents, such as for instance the macroporous walls formed by a deformable wire mesh allowing diametral retraction for introduction of the stent into air or food pipes and expansion therein for dilatation, or repair, or bridging of said pipes, have the disadvantage that they permit ingrowth of tumors and other rapid growth cells through the wire mesh or discontinuous wall, with the resulting risk of stent occlusion.
For preventing ingrowth of cells through the stent, the document DE-3918736-A1 describes an expandable metallic stent with an inner Teflon.RTM. tube affixed to the stent by suture or pressure, or an inner tube and an outer tube, both of Teflon.RTM., connected pouch like to each other. At least in case of degradation of the inner tube, there will be a strong risk of having flaps from the inner tube occluding the vessel, or migration of the inner tube with respect to the stent and a further risk of occlusion of the vessel. Furthermore, the absence of resiliency of Teflon.RTM. does not allow constriction and expansion of the stent without additional place consuming measures such as zig-zag folds of the Teflon.RTM. tubes.
The document "Endoscopy 1992:416-420" also describes an expandable metallic stent for preventing ingrowth of malignant structures. This stent, formed by an expandable wire mesh, is covered by a silicone membrane or skirt which surrounds a portion of its length.
This membrane or skirt is secured around the stent by suture of its ends to the wire mesh, and, in situ, the membrane is thus radially held in place between the stent wall and vessel wall. To have the membrane or skirt positioned between the stent wall and vessel wall is advantageous in case of degradation of the membrane. However, such a coverage of the stent is far from being effortless and mostly will have to be done by hand, which will require skills. In addition, it is limited to certain types of materials and it may prove fragile, being possible to have the membrane or skirt getting loose from the wire mesh, which may allow relative movement between the membrane and the stent, with the resulting risk of occluding the vessel.
The object of this invention is to avoid the aforesaid drawbacks.
To this effect, the stent and methods in accordance with the invention comply with the definitions given in the claims.
In that way, the continuous covering layer is closely bound to the discontinuous structure which it covers and there is definitely no risk of separation therebetween. And even in the case of a strong degradation of the covering layer in course of time, there cannot be any migration of the covering layer with respect to the discontinuous wall of the stent because of the aforesaid intimal interconnection. Furthermore, the liaison of the covering layer with the discontinuous wall of the stent eliminates any delicate, time and skill consuming efforts and allows coating of any kind of discontinuous expandable stent wall.
In sum, the present invention relates to a stent with a discontinuous expandable wall and a continuous covering layer of elastic material surrounding the discontinuous wall. The continuous covering layer of elastic material is adhered to the discontinuous wall so it is intimately united with said discontinuous wall. The continuous covering layer of elastic material may extend at least partly radially within the discontinuous wall of the stent, and may extend around and inside the discontinuous wall of the stent. The continuous covering layer may be adhered to the discontinuous wall by means of a binder, or it may be heat adhered or chemically bonded to the discontinuous wall. The continuous covering layer may be adhered to the discontinuous wall by radial pressure of the discontinuous wall against the continuous covering layer. The continuous covering layer may have a structured surface towards the discontinuous wall, wherein the continuous covering layer is adhered to the discontinuous wall as a result of said structured surface.
The present invention also relates to a method for applying a covering layer to a stent by radially contracting the stent; inserting at least a portion of the contracted stent into a tube the inner surface of which has been previously done over with a lifting medium; allowing the stent to radially expand in the tube; wetting the assembly tube plus stent with an elastomeric polymerisable composition dissolved in a sufficient amount of solvent to permit wet forming; evaporating the solvent; polymerizing the elastomeric composition in the tube; and taking the layer covered portion of the stent out of the tube. The tube, the inner surface of which has been done over with a lifting medium, may be first wetted along with the elastomeric composition added with solvent. The solvent may be evaporated before the step of insertion of the stent into the tube.
The present invention also relates to a method for applying a covering layer to a stent by doing over a roll on surface with a lifting medium; coating said roll on surface with an elastomeric polymerisable composition dissolved in a sufficient amount of solvent to permit contact forming; rolling at least a portion of the stent in expanded condition on said coated roll on surface; withdrawing the stent from the roll on surface; evaporating the solvent; and polymerizing the elastomeric composition adhered by contact on said portion of the stent.
The present invention also relates to a method for applying a covering layer to a stent by forming a tube of predetermined length with an elastomeric polymerisable composition; radially contracting the stent; inserting into the tube a portion of the stent corresponding to said predetermined length of the tube; allowing the stent to radially expand in the tube, and welding the surfaces of contact between the stent and the tube.
The present invention also relates to a method for applying a covering layer to a stent by forming a tube of predetermined length with an elastomeric polymerisable composition; coating the inside of the tube with an adhesive medium; radially contracting the stent; inserting into the tube a portion of the stent corresponding to said predetermined length of the tube; allowing the stent to radially expand in the tube; and allowing the adhesive medium to cure.
The present invention also relates to a method for applying a covering layer to a stent by forming a tube of predetermined length with an elastomeric polymerisable composition; coating the inside of the tube with an elastomeric polymerisable composition dissolved in a sufficient amount of solvent to permit contact forming; radially contracting the stent; inserting into the tube a portion of the stent corresponding to said predetermined length of the tube; allowing the stent to radially expand in the tube; evaporating the solvent; and polymerizing the elastomeric composition adhered by contact to the tube and to the stent.